Carpet recycling has the potential to be of significant benefit, both environmentally and financially. At present many waste carpets are sent to landfill, which is undesirable as many of the materials used to make carpets are not biodegradable. Reuse of the materials reduces the amount of waste carpet which is sent to landfill. In addition, some of the constituent materials of carpets are costly to make or obtain, and accordingly there is a need for methods of recovering and reusing them.
The present proposals are applicable to the processing of any waste material, especially in layer form, containing more than one constituent material with at least one of them being fibrous. Typical flooring materials (carpets, matting) are constructed from constituent materials which include fibres. For example, carpet may be formed from woven fibres in which the weft lies flat, while the warp is looped to form an upstanding pile on the surface. Some woven carpets have a backing layer to stabilise the carpet, which may be for example a layer of adhesive. An alternative is “tufted” carpet which may have fibre tufts mounted into a primary backing fabric, which may be woven or non-woven. A bonding agent may anchor the tufts, and this bonding agent may be on a secondary backing fabric, which again may be woven or a non-woven such as felt. Carpet tiles are often similar to tufted carpets, except that the secondary backing is usually stiffer and not fabric, e.g. PVC or bitumen.
In general, typical materials for processing by the present methods (“materials of the kind described”) comprise a combination of (a) fibre material—as (i) tufts or pile, and/or (ii) one or more fabrics, woven or non-woven—with (b) polymer-based matrix material which may be present (i) as or in one or more generally continuous layers (e.g. backing layer) and/or (ii) as a binder or adhesive in relation to fibre, and/or in relation to particulate material such as filler. Such materials may be waste carpet, mats, carpet tiles, matting, underlay or the like. For convenience the term “carpet” is used herein to comprehend these latter general types unless a specific context indicates otherwise.
It is known for materials recovered from waste carpet to be used in various ways. In a “closed-loop” recycling system, recovered materials are used to make a product similar to that they were recovered from. For example, carpet polymer backing and yarn (fibre) may be separated, broken down and reprocessed. The reprocessed backing material may be used in new carpet backing, and the reprocessed yarn made into more carpet facing. This recycling can be repeated more than once, depending on the materials. For example, carpet manufacturers already reuse nylon-6 (polycaprolactam) recovered from the fibres of waste carpet, to make new carpet fibre. Alternatively recovered materials may be reused to make different products: “downcycling”. For example, nylon-6,6 recovered from carpet may be used to manufacture car parts, although most continues to go to waste (landfill). In any event, potentially recyclable material such as nylon-6 or nylon-6,6 needs to be recovered from waste carpet and isolated in a good usable state.
A variety of methods for the separation, recovery and reuse of constituent materials of carpet have been described. EP-A-0759456 exemplifies solvent-based methods, extracting polyamide from carpet residues using an extraction agent containing aliphatic alcohol. U.S. Pat. No. 5,535,945 describes reclaiming polymer fibres from carpet by shredding the carpet into strips and disintegrating the strips by hammering them against anvil elements.
U.S. Pat. No. 6,126,096 describes soaking used carpet pieces, chilling them to stiffen the backing material, and introducing the carpet pieces into a cyclonic comminuter which reduces the carpet pieces with separation of fibres from backing. The pre-soaking is disclosed as enhancing the separation of the component fibres in the comminuter, and also as initiating breakdown of latex backing.
U.S. Pat. No. 5,704,104 describes separation of pile and backing material of used carpet using dry ice pellets to freeze the binder material (usually latex) to a temperature that makes it brittle and easier to break up. The pellets also serve as abrasive agents, avoiding liquid or gritty residue because the pellets sublimate. The avoidance of using steam, chemicals or liquids is said to be advantageous to avoid the deposition of unwanted residues.
In view of the above, the aim or object of the present proposals is to provide new and useful methods for processing materials of the kind described, particularly with a view to the recycling of one or more constituent materials thereof. Preferred aims include economical and effective methods, adaptable for use with a variety of carpet materials and structures, which can be implemented without undesirable mess and waste, and which enable desired components such as polymeric fibres to be isolated without chemical deterioration.